Managing Populations, Retaining Squares Are Keys to Plant Bug Control

No surprise here. Thanks to boll weevil eradication and the advent of transgenic insect traits for cotton, plant bugs have emerged as the most important pest in many Cotton Belt states.

The 2013 summary of Cotton Insect Losses compiled by Mississippi State University showed that the highest percentage of insect losses in cotton nationally came from plant bugs, leading to an estimated loss of 188,520 bales. The study also showed that infested acres received, on average, more than 3.5 treatments for plant bugs. For Mid-South states, however, the number of treatments per season can range from six to 12 to more.

The insect’s ability to rapidly increase populations can often seem overwhelming for growers and consultants. But recent studies showing decreased efficacy on plant bugs from many labeled insecticides are also troubling.

“We reviewed data from about 43 trials conducted in Arkansas over the past 2-3 years and looked at the percent control for the different products we had in those trials,” said Gus Lorenz, University of Arkansas Extension entomologist, speaking to a consultants conference in Memphis. “Seventy percent control was the best we could see with single product applications.

“I tell growers we don’t control plant bugs,” he continued. “We manage them. That 70 percent control may be very adequate early season before we go into bloom and those early plant bug populations take off. It may get the numbers down to where growers can maintain square retention. I’m truly not concerned about how many plant bugs I can control with a treatment. Our goal is 80 percent square retention.”

Lorenz and other Mid-South Extension entomologists have worked together to develop sampling techniques for plant bugs, as well as a common treatment threshold of three plant bugs per five row feet. That provides a good guideline for growers and consultants, especially during the key period between late squaring and the fourth week of flowering, when plant bugs can do the most damage to yields. But recent history has shown that plant bug populations can blow through a threshold and never look back.

“In our plot work, we see plant bug numbers going from 2-3 per five row feet to 60 per five row feet in a matter of 4-5 days,” stated Lorenz. “That’s how quickly it’s happens to us, and that’s how quickly it’s happening on a farm.

“If growers wait too long to make an application and knock that number down below the threshold, they’ll have to come back with another treatment pretty quickly,” he said. “A lot of growers don’t want to spray more than once a week, and I understand that. But it’s tough when plant bugs are going exponential on us. If you don’t hit them quickly, you can get into trouble.”

Rotation – as well as close attention to nozzles and application systems and timing – is the key to plant bug management. Treatment recommendations now focus on a mix of products to help protect effectiveness and keep plant bug numbers below threshold.

Diamond is a good fit during the late squaring/early flowering time period, when large numbers of adult plant bugs are usually migrating into cotton from corn or other wild hosts. But, noted Lorenz, a tankmix of Diamond and Centric can provide an additional punch if growers are trying to knock high numbers of plant bugs down to a more manageable level.

Follow with Transform during early flowering. “Transform provides a new mode of action that has shown a higher level of control than we see with some other products,” said Lorenz.

Growers can then keep focus on continuing management with tank mixes of organophosphates and pyrethroids.

“Many growers tend to rely on acephate followed by acephate followed by acephate,” stated Lorenz. “It works great, and it’s inexpensive. But you risk losing efficacy in that situation.

“Likewise, bifenthrin by itself is not very good on plant bugs,” he continued. “But later in the season, it seems to be one of the products of choice and has shown striking increases in control when put in a tankmix.”

However, warns Lorenz, some tank mixes just don’t work. Getting the right tankmix partners together is the key.

Growers also need to keep an eye on rate limits for many of these products.

“There are concerns about rate limits with some products,” said Lorenz. “For example, we’ve seen acephate rates jump from a third of a pound per acre to one pound per acre in a little over five years. When you see that kind of rate shift over a short amount of time, we can get in trouble with some of these products. That’s why it’s vitally important for us to make our technologies work and last as long as we can.

“We need to maintain everything we have to keep that control of plant bugs.”

At a time when growers rely increasingly more on genetic advancements in yield and fiber quality to keep cotton economically viable, cotton breeders and researchers are excited about the possibilities that genome mapping brings to variety and trait development.